Recently there have been several developments in the field of metal foil supported catalytic media. An early development in metallic carriers for catalysts is described in U.S. Pat. No. 1,636,685 dated 26 July 1927 to Downs. Here metallic (iron) particles are treated by dipping into melted aluminum. An alloying action takes place between the aluminum and iron. The resulting surface is very satisfactory for the deposition of catalytic materials such as a metal of Group V or Group VI of the Periodic Table. Such structures are adapted for vapor phase catalytic oxidation of organic compounds.
U.S. Pat. No. 2,658,742, dated 10 Nov. 1953, to Suter et al discloses a metallic catalyst support for removing harmful ingredients from exhaust streams. Platinum and palladium are disclosed as useful to aid in oxidation of combustible materials, e.g., carbon monoxide. Stainless steel is disclosed as a base metal for the catalyst.
Bernstein et al U.S. Pat. No. 3,773,894 disclose a metallic catalyst supported on a metallic substrate as a catalytic converter for internal combustion engine exhaust gases. Various physical forms of the catalyst support are shown including spiral wound screen and cordierite honeycomb.
The U.S. patent to Retallick No. 4,301,039, dated 17 Nov. 1981, discloses a method of making a metallic catalyst support in a spirally wound form whereby indentations in the surface of the metal foil will not nest together.
U.S. Pat. No. 4,318,888, dated 9 Mar. 1982, to Chapman et al discloses a spirally wound foil structure having a corrugated surface and distinct different catalysts supported on confronting surfaces.
U.S. Pat. No. 4,402,871 to Retallick, dated 6 Sept. 1983, discloses a honeycomb catalyst support formed by folding a single layer of metal foil back and forth upon itself in an accordion or zig-zag fashion. Each layer in the honeycomb has indentations of uniform height so that the spacing between layers is equal to this height. A different pattern of indentations is used on alternate layers and the indentations are on opposite sides of the strip in alternate layers. This structure prevents nesting of confronting layers.
More recent structures are made of a thin ferritic stainless steel of the type referred to by Kilbane in patent application Ser. No. 741,282, filed 4 June 1985, now U.S. Pat. No. 4,686,155, and by Retallick in application Ser. No. 738,485, filed 28 May 1985, now U.S. Pat. No. 4,601,999, corrugated and fan folded or folded back and forth upon itself. The surface of the strip is provided with a catalytically active agent for decontaminating an exhaust gas, e.g., the exhaust gas generated by an internal combustion engine. Reference may also be had to Cornelison patent application Ser. No. 796,710, filed 12 Nov. 1985, now U.S. Pat. No. 4,725,411, which discloses a catalytically active fan folded element of the type which can be produced by the process disclosed in the application of Cornelison and Retallick, Ser. No. 830,698, filed 18 Feb. 1986, now U.S. Pat. No. 4,711,009.
Thus, it will be seen that the general type of catalyst support element to which the present invention relates is generally well known. It has now been found that there is a special relationship between the parameters defining the corrugated surface that when observed provides a stack of corrugated foil which is uniform and has no weak areas.